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https://issues.apache.org/jira/browse/HBASE-5689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13247960#comment-13247960
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Ming Ma commented on HBASE-5689:
--------------------------------
Really nice finding and fix. Some comments regarding performance:
1. replayRecoveredEditsIfAny still sorts and uses the sequence id of next
recoverededit file as the max sequence id of the current recoverededit file.
With this fix, is that still necessary? replayRecoveredEditsIfAny can simply
walk through all the recoverededit files and skip those files that have "max
sequence id" <= "current sequence id of the region".
2. If we have multiple recoverededit files for a given region, is it safe to
say that "In maximum, there could only be one recoverededit file whose max
sequence id is larger than the current sequence id of the region"? If yes,
replayRecoveredEditsIfAny can skip the rest of recoverededit files once it
detects that special recoverededit file.
> Skipping RecoveredEdits may cause data loss
> -------------------------------------------
>
> Key: HBASE-5689
> URL: https://issues.apache.org/jira/browse/HBASE-5689
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 0.94.0
> Reporter: chunhui shen
> Assignee: chunhui shen
> Priority: Critical
> Fix For: 0.94.0
>
> Attachments: 5689-testcase.patch, HBASE-5689.patch, HBASE-5689.patch,
> HBASE-5689v2.patch
>
>
> Let's see the following scenario:
> 1.Region is on the server A
> 2.put KV(r1->v1) to the region
> 3.move region from server A to server B
> 4.put KV(r2->v2) to the region
> 5.move region from server B to server A
> 6.put KV(r3->v3) to the region
> 7.kill -9 server B and start it
> 8.kill -9 server A and start it
> 9.scan the region, we could only get two KV(r1->v1,r2->v2), the third
> KV(r3->v3) is lost.
> Let's analyse the upper scenario from the code:
> 1.the edit logs of KV(r1->v1) and KV(r3->v3) are both recorded in the same
> hlog file on server A.
> 2.when we split server B's hlog file in the process of ServerShutdownHandler,
> we create one RecoveredEdits file f1 for the region.
> 2.when we split server A's hlog file in the process of ServerShutdownHandler,
> we create another RecoveredEdits file f2 for the region.
> 3.however, RecoveredEdits file f2 will be skiped when initializing region
> HRegion#replayRecoveredEditsIfAny
> {code}
> for (Path edits: files) {
> if (edits == null || !this.fs.exists(edits)) {
> LOG.warn("Null or non-existent edits file: " + edits);
> continue;
> }
> if (isZeroLengthThenDelete(this.fs, edits)) continue;
> if (checkSafeToSkip) {
> Path higher = files.higher(edits);
> long maxSeqId = Long.MAX_VALUE;
> if (higher != null) {
> // Edit file name pattern, HLog.EDITFILES_NAME_PATTERN: "-?[0-9]+"
> String fileName = higher.getName();
> maxSeqId = Math.abs(Long.parseLong(fileName));
> }
> if (maxSeqId <= minSeqId) {
> String msg = "Maximum possible sequenceid for this log is " +
> maxSeqId
> + ", skipped the whole file, path=" + edits;
> LOG.debug(msg);
> continue;
> } else {
> checkSafeToSkip = false;
> }
> }
> {code}
>
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